B Unicellular organisms communicate with neighbors or the environment Fig 9 1a Chapter 9 Cell Communication 9 1 I 1 Communication Introduction Pupillary Reflex A Definitions to signals 2 Signal a Ex a molecule ligand a force light any agent that affects a cell producing detecting and or responding i Ligands bind to receptors noncovalently a cellular structure usually a protein that 3 Receptor responds to a signal II When a cell receives a signal Fig 9 3 A Receptor Activation B Signal Transduction conversion to a different form C Cell Response to the signal transcription D Termination of Response 1 Ex enzyme activation cytoskeletal change or III Types of cell signaling Fig 9 4 A Endocrine 1 Signals travel long distances through the bloodstream 2 Signals are called hormones B Paracrine signaling C Autocrine signaling 1 Signaling cell lack receptors target cell is local 1 Signaling cell receives its own signal 2 Ex Looking in a mirror D Juxtacrine signaling 1 Contact dependent 2 Cell that produces the signal must directly contact receptor cell to communicate signal never enters extracellular space 3 Ex Development of a zygote IV Ligand Receptor Activity 9 3 9 4 A Cell surface receptors interact with molecules that can t diffuse across membrane Fig 9 6 B Signals that do diffuse across the membrane bind to intracellular receptors fig 9 6b C Clicker question Ligand type of receptor intra vs extracellular 1 Tryptophan extracellular 2 ATP extracellular 3 Estrogen intracellular all steroids diffuse through membranes 4 Insulin extracellular 5 Adrenaline extracellular D ATP can be released as a signaling molecule 1 3 types of ATP receptors a P1 P2X P2Y 9 6 V 3 classes of cell surface receptors GPCR s Enzyme Linked Ligand Gated Ion Channels A G Protein Coupled Receptors G P C R 1 Associate with other proteins when activated 2 5 steps of G P C R Activation Fig 9 7b 9 8 1 Signal binds to G P C R 2 G P C R changes shape binds to G protein complex 3 G protein releases GDP from its 4 GTP binds to the 5 G protein complex dissociates breaks apart activated subunit propagates response subunit taking the place of GDP subunit 3 When GTP binds to a protein the protein changes shape B Enzyme Linked Receptors Fig 9 7c 1 When activated catalyze reaction a Usually phosphorylate cytosolic protein b Fig 9 7c receptor proteins dimerize to form 2 part structure then phosphorylate a target protein C Ligand Gated Ion Channels Fig 9 7d 9 7 9 8 VI Amplifying Signals Secondary Messaging A Initial signal can be amplified B Signal ligand 1st messenger binds to receptor C Small molecules ions 2nd messengers are produced which convey information in cell 1 2nd messengers allow signal amplification a speedy response D Ex Adrenaline binds to a G protein coupled receptor in heart muscle fig 9 9 enzyme that phosphorylates another molecule 3 Signal amplification can occur at many levels 1 Second messenger cAMP cyclic AMP 2 Kinase a Phosphorylaton activation a At each step the signal amplitude is increased exponentially i e 2 4 8 activated G s activates adenylyl cyclase activated adenylyl cyclase converts ATP into cAMP cAMP activates protein kinase A PKA PKA activates target proteins like CREB Adrenaline noradrenergic receptor in membrane subunit of G protein 4 Pathway Fig 9 10 E cAMP is a common 2nd messenger 1 Nucleotide 2 Synthesized from ATP 9 9 9 10 Fig 9 11 VII Turning Off Signals A Example 1 Enzymes convert cAMP to AMP stops signal transduction pathway 2 Other enzymes Phosphatases remove phosphate groups from proteins 3 Pumps sequester ions VIII Cell s Proteome Determines Cell Response A Proteome set of proteins produced by a cell 1 All cells have same genome but produce different proteins B Receptor protein required for response C Receptor type and response can have different 1 Signal binding affinities 2 Signal transduction pathways STPs 3 STPs that cause different results
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